Venezuela’s oil output, already the lowest since 2009, is set to slide further this year as contractors scale back drilling after the cash-strapped country fell more than $1 billion behind in payments.The Latin American nation’s oil production, which generates 95 percent of export revenue, will decline by about 11 percent to 2.1 million barrels a day by the end of the year, Barclays Plc estimates. Output is falling largely because oil-services companies aren’t being paid, according to the International Energy Agency.